Obscured by Clouds. The rough and ready blog of a cloud benighted biologist and amateur astronomer. Astroblog will cover my interests in astronomy, biology and Life, the Universe and Everything.

Friday, May 20, 2011

What makes a bright comet? The case of Elenin and Cassini at Saturn

Elenin "near" Saturn in 2009, click to embiggen.

When an astronomer says a comet is “bright”, it means that the comet will be brighter than magnitude 12. At this magnitude, the comet will be visible to the eye in moderate aperture amateur telescopes, rather than requiring substantial exposure times with film of CCD cameras. To the ordinary person on the Clapham Omnibus, this is still extremely faint; people with good eyesight under ideal dark sky conditions can see objects as dim as magnitude 6.6, over 100 times brighter than a magnitude 12 object.

Cassini in orbit around Saturn with the location of Elenin shown, Elenin is too dim to be seen, click to embiggen

Not surprisingly, the astronomical use of “bright comet” can cause considerable confusion, especially as most people don’t have a good feel for the brightness of objects in the sky. Comet C/2010 X1 Elenein is a “bright” comet; although it is currently around magnitude 14, it will reach a magnitude of somewhere between 6 (just visible to the unaided eye) and 4 (about as bright as epsilon Crucis, the 5th and dimmest star in the Southern Cross) at its brightest.

Why the variation? The brightness of an object like an asteroid depends on how big it is, how far it is from the Sun and us, and how shiny it is. Calculating the brightness of an asteroid at closest approach is fairly straightforward, even if we are a bit uncertain about how shiny and big it is.

Gustavo Muller's image of Elenin on August 8, 2011, from the Aerith gallery.

Unlike asteroids, we are not seeing the surface of the comet per se (except when it is very, very far from the Sun), but light reflected from the tenuous haze of dust and gas that boils off the “dirty snowball/icy dirtball” that is a comet. The coma of a comet can extend many thousands of kilometres from the surface.

The Great Comet was around 30km in diameter and had a coma nearly as big as the Sun, comet Halley is 6x15 km and had a coma 100,000 km wide when it last approached Earth, C/2010 X1 Elenin is roughly 3-4 Km and has a coma around 50,000 km wide. The coma is a pretty good vacuum by Earth standards, but there is enough dust and fluorescing gas in this thin haze to make the comet glow brighter than the mere iceball would.

How bright the comet is depends an exactly how active it is (ie how much dust and gas it produces and the size of the coma), which depends on a complex set of properties (if there are lots of rifts in the organic/silicate crust that coats the comet surface to blast out dust and gas, for example). We don’t have an exact handle on exactly what makes a comet bright, and there is substantial discussion on the comet lists about the best way to estimate the development of cometary brightness.

However we have a number of good rules of thumb. Comets that have just dropped in from the Oort cloud, like Elenin, are intrinsically dim. That is they tend produce much more gas than reflective dust and usually do not put on much of a show.

Again, there have been exceptions, comet 2006 P1 McNaught was initially expected to be very bright, around magnitude 2, but ended up around an astounding magnitude -1 when we could first see it again after it passed behind the Sun (although it’s brightness dropped rapidly after that). Still by following the light curve of a comet we can get a good idea of its brightness. The light curve of Elenin is still developing, but it looks on track to be somewhere between just visible to the unaided eye to being dimly visible.

People also confuse the concept of “bright” in terms of a comet and “big”. And example is here:

Elenin passed fairly close to Saturn in Mid-Late 2009. Cassini was in the area, taking pictures of Saturn and it's moons. It had just wrapped up its scheduled mission when project planners extended it.[snip images]So a big comet was nearby, and Cassini never saw it? This means either:A) NASA saw Elenin with Cassini in 2009 (or earlier) and decided not to tell usB) NASA did NOT see Elenin in 2009 because it's not really a bright comet after allC) NASA did NOT see Elenin in 2009 due to chance or incompetence.

Rings of Saturn as seen from Cassini. See the Stars? No, they are all washed out in the image (click to embiggen)

Now there is a couple of issues here, “fairly close” was a large chunk of 1 AU away, what looks “close” on a JPL animation is still an enormous distance way (see the image at the top of the post). And again, the mistaken concept of “bright”. At the time (2009) Elenin was still fairly dim, around magnitude 22, just a tiny bare lump of ice with only the faintest traces of a coma around it, far from the illumination of the Sun.

You can use the JPL horizons program to find out how bright it would seem from Cassini. Turns out it’s around magnitude 22 as well (the comet was closer, but as seen from Saturn and Cassini it would only be partially illuminated).

Spica as imaged by the Cassini cameras (click to embiggen)

Now have a look at the typical image from Cassini (see above), can you see the background stars? No, Cassini is photographing relatively bright objects, and the typical exposures are too short for all but the brightest stars, let alone a dim comet.

Occasionally the spacecraft does do a long exposure image of the stars, for navigation purposes. The image to the left is just such an image centered on Spica, (alpha Virginis). The dimmest star in this image is magnitude 9, well above the brightness of Elenin. Even if a navigation image has been taken which had been pointing in Elenins direction (in general Cassini wasn’t pointing anywhere near Elenin), it couldn’t have picked the comet up.

NASA’s failure to pick up Elenin is not due to incompetence, bright comets are not bright for their entire journey around the Sun, but typically brighten substantially only during the closest approaches to the Sun, in principle Cassini could not have picked the comet up. Elenin won’t be spectacular, but at the very least will look nice through binoculars under a dark sky.

Wallace Thornhill's Electric Comet theory says "For many decades, astronomers have held firm to the position that comets are loose aggregations of ice and dust, typically characterized as "dirty snowballs." The very fact that some comets can fly so close to the sun before disintegrating seems a logical challenge to the dirty snowball model."

He says "...the comet’s brightness depends on electrical energy from the Sun’s circuit..."

The negatively charged comet is interacting with proton flow coming from the sun causing huge plasma discharges, thus creating its brightness, which increases as it nears the sun.

Elenin is a very dangerous comet because it is a long period comet whose tail will blast the Earth with photons. Comets are not balls of ice and dust like Nasa states. Nasa will not release this information because there is absolutely nothing anyone can do about it except panic.

Comets are electric space capacitors. Comets are electromagnetically connected to the sun and planets by EM ropes (JP, 2005). Extreme EM can cause earthquakes. This is what HAARP can do. EM energy lubricates fault lines. The reason Elenin is causing quakes when others do not is because Elenin has been in deep space a long time gathering electrons to feed the sun by discharging its capacitance.

Comets pick up electrons as they fly through space. The longer in space without discharging, the more electricity is stored in the comet. When the comet approaches the sun, it begins to glow because the electric circuit is energized by the sun’s proton wind. The sun provides the positive charge and the stored electrons provide the negative charge to complete and electric circuit. The comet nucleus behaves similar to the filament on a lightbulb when positive and negative wires are attached. The bulb glows.

Comets do the same thing when the comet discharges its capacitance. The infrared signature for comet Elenin suggest the charge Elenin is carrying is so large that when the comet dumps its capacitance, the resulting photon flare up will engulf the Earth as the Earth passes through the tail. When Elenin was 14 AUs away on June 14, 2007, Nasa photographed the comet when they took the infrared image for google sky. The infrared image indicates Elenin’s infrared electrical signature is 17 million miles across with xray jets extending over 100 million miles from Elenin. When Elenin flares when it dumps its energy, the photon blast will be so great that it will instantly turn everything on the earth’s surface to light energy.

The reasons other comets are not a threat is that most comets do not pass between the earth and the sun putting the earth in the tail. Also, comets with periods of a a hundred years or so are able to dump their charge more frequently which keeps the IR signature low. Elenin is different. There is no other object is space that humans have identified that has an electric signature like Elenin.

Sigh, Earth is blasted by photons every day, far more than any comet can. Earth has been through bigger and better comets tails before, including Halley's comet and the Great Comet of 1861. Nothing happened then, nothing will happen now.

Sigh, Earth is blasted by photons every day, far more than any comet can. Earth has been through bigger and better comets tails before, including Halley's comet and the Great Comet of 1861. Nothing happened then, nothing will happen now.

Haley's comet has a period of 76 years. Haley is not in deep space long enough to build up enough capacitance to cause damage to earth. If you look at Haley's infrared image, you will see it does not carry as a strong charge as compared to Elenin. NO modern man has ever seen a comet like Elenin. Yes, the earth is blasted with photons everyday, but nothing like the energy that Elenin exhibits in the Nasa googlesky photo. Not even the sun emits such a strong infrared image. Its funny that people sigh and show their ignorance before they check the facts. Comets are cosmic wrecking balls and not the fluffy balls of ice you have been lead to think. But hey, lets not argue. You will get a sign on 7/7. Watch Saturn and you will see more evidence.

Anonymous wrote: Haley is not in deep space long enough to build up enough capacitance to cause damage to earth. The great comet of 1861 was, and didn't. The IRAS image in Google Sky is the carbon star CW Leonis, not Elenin.

Ian,I agree the infrared image may appear to be CW Leonis. However, most calculations involve the distance to the star that are based on redshift.

The redshift quasar issue suggests that redshift based distance calculations may be flawed. If redshifted quasars that should be billions of light years away are really many orders of magnitude closer. then redshift based calculations for CW Leonis could be wrong by many orders of magnitude as well.

Until the quasar redshift and time dilation riddles are solved, redshift calculations can not be trusted. If these can't be trusted, then other calculations that use distance can't be trusted either.

CW Leonis has been studied for decades by multiple observers with a whole range of Earth and space based telescopes.

It hasn't moved in over 40 years. Its parallax measurements are consistent with redshift measurements in that it as to be at least 120 parsecs away. If CW Leonis was closer than 10 lightyears we would have noticed this long ago.

Yes Ian. You would have noticed it long ago using the same redshift technology that indicates quasars are billions of light years away. Now that redshift calculations have been proven to be unreliable, how can we trust yours and others calculations based on redshift? WE CAN'T.

We also can't rely on brightness calculations to determine size. All cosmic bodies are not alike. The earth is different than any other planet and our moon is different than others like Titan, so how can we assume all comets are the same and have the same light propagating properties? WE CAN'T. Astronomy is showing its ignorance.

So, not only are most distance calculations now suspect as being wrong, but all size calculations based on brightness are most likely flawed as well.

Based on this, the image on google sky that you call CW Leonis could very well be something else much closer. It is a fact that this object appears as the brightest object in the sky in infrared. Redshift puts it about 600 light years away, but if we assume redshift is flawed and consider this object within our solar system, its size becomes extremely smaller and its infrared signature is less than 10 million miles across.

When a method is flawed and is continued to be used by professionals who know it is flawed, one must question the sanity of the professionals.

If I was the captain of a ship and I knew my ship has big whole in it, I would be called crazy for sailing.